View - Kowalewski, M. - Virginia Tech

WALKER AND BRETT—POST-PALEOZOIC PATTERNS IN MARINE PREDATIONcreatures for food and ornamentation for manythousands of years based on archaeological shellmiddens (e.g., Speed, 1969; Avery and Siegfried,1980; Jerardino et al., 1992). For example, in Chile,the rocky coast has been exploited by humans forfood for at least 8,500 years (Moreno, 2001). Thisforaging was tied closely to settlement of thePacific region of South America, and has onlyrecently been recognized as a force that affects theresultant ecological community structure of an area(Moreno et al., 1984). Ecological shifts in seafoodbiota directly or indirectly caused by humans areknown from the present day (Castilla and Duran,1985; Castilla, 1999) and from the stratigraphicrecord (Simenstad et al., 1978; Kirch, 1983).EVOLUTIONARY VIGNETTES:SELECTED PATTERNSOF PREDATIONFROM THE CENOZOICThe Mesozoic Marine Revolution hypothesis(Vermeij, 1977, 1987) has been subjected to manytests, from several sources of evidence, chiefly todetermine: (1) if shell armor increases through time;(2) if shell predators increase through time; and (3)if lethal shell injuries increase through time (see alsoVermeij, 1983). In the following sections we reviewand critique some of the primary lines of argument.Most of the putative durophagous functional groupsre-evolved in the Cenozoic, and, one could argue,became more common during this time than in theMesozoic. However, some of this apparent increasemay represent biases such as the Raupian “pull ofthe Recent” and the better record of well-preservedfossils. It is also well known that aragoniticMesozoic invertebrates, especially molluscs, are notas well preserved as calcitic forms (except forammonoids in black shales); whereas in theCenozoic more aragonitic forms are preserved,giving us a more detailed picture of the potentialpredatory panorama. Shell repair, drilling, and otherfeatures can be distinguished on Cenozoic hardpartsmuch more easily than on older ones. This is not agloom-and-doom scenario, just a realistic one.Examples of prey in coprolites or regurgitatedremains, predation preserved in situ, and preyorganisms in stomach contents are rare inCenozoic deposits just as they are rare inMesozoic and Paleozoic assemblages (Häntzschelet al., 1968; Boucot, 1990; Brett, 1990). Whilethere is an extensive literature on coprolites, moststudies focus on terrestrial and vertebrate remains;few if any coprolites in marine environments canbe tied with reliability to a specific predator(Bishop, 1975; Boucot, 1990).Echinoderms.—In many localities, not least inthe Danish basin, the Cretaceous-Tertiary extinctiongreatly affected the invertebrate biota. However,several echinoderm groups do not appear to havebeen greatly affected by this extinction event, andshow an increase in diversity directly above theboundary in the Danish basin (Kjaer and Thomsen,1999). There are several examples of shallow-waterstalked crinoids from the early Cenozoic (Oji, 1996);and further movement offshore of isocrinid (stalked)crinoids occurred in the Miocene in the Caribbeanregion (Bottjer and Jablonski, 1988; Donovan,2001). Deeper-water crinoids have a relativelyconstant generic composition from the Miocene tothe Recent; the Plio-Pleistocene regional extinctionhad little effect on this group (Donovan, 2001).Shallow water areas remain populated by stem-lesscomatulid crinoids (Donovan, 2001). This suggeststhat mobility and cryptic habitats may have enabledthis group to survive in the face of high predation inshallow water.Arm autotomy is common in stalkless crinoids,but has not been well documented in stalkedcrinoids (Oji, 1986). The ability to autotomizecrinoid arms dates back at least to the Triassic (Ojiand Okamoto, 1994). It is thought that autotomyacts as a “lizard-tail” defense (after Baumiller etal., 1999): arms can be dropped quickly into themouths of predators, while the main body of thecrinoid is left to regenerate new arms. It is possiblethat isocrinids exploited this ability and that this iswhat allowed them to survive the putative increasedfish predation in the late Mesozoic (Oji andOkamoto, 1994). Modern crinoids from bathyaldepths have more regenerated arms than crinoidsfrom deeper depths (Oji, 1996).167